Manufacturing chlorates.



No. 76,789. Patented DBG. 23, |902.

R. Tilli..FALL.

MANUFAIU-Rmf QHLORATES.

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BIRMINGHAM, ENGLAND.

MANUFACTURING C'HLORATES.

SPECIFICATION forming part of lLetters Patent No. 716,789, dated December 23, 1902.

Application filed May 2,1902. Serial No. 105,683. (No specimens.)

To a/ZZ whom it may concern:

Be it known that I, RICHARD THBELFALL, a subject of His Majesty the King of Great Britain, residing at 30 George road, Edgbaston, Birmingham, England, have'invented an Improved Method of Manufacturing Chlorates and Perchlorates of the Alkali Metals, of which the following is a specication.

In the electrolytic manufacture of chlorates and perchlorates of the alkali metals Without a diaphragm and with and Without the addition of potassium or sodium chromate or bichromate to the electrolyte, consisting of a neutral or slightly alkaline solution of the chlorids, it is found that the efticiency of chlorate production in practical working rapidly falls o as the electrolysis continues compared with that which theoretically should be obtained from the current employed.

It is of course well known to chemists that a current of electricity of about .2 amperes per square centimeter of electrode surface driven through an electrolyte composed of strong neutral solutions of the chlorids of the alkalimetals at apressure of about three volts will decompose the electrolyte and yield hydrogemcxygen, hypochlorites, chlorates, and traces of chlorin.

In the manufacture of chlorates, for which this invention is more particularly intended, (although by continuing the electrolytic ac-Y tion perchlorates may be produced,) I have found that in order to keep the chlorate production at a high level of efciency it is necessary to have in solution a certain amount of free hypochlorous acid, and the present invention relates to a method of attaining that end both conveniently and economically; and it consists, essentially, in subjecting the electrolyte from which the chlorates or perchlorates are to be derived to unequal electrolytic action at the anode and the main cathode, respectively, the action over and above that passing to the main cathode being diverted from the main circuit and greatest at the anode, the excess quantity of current being employed in the formation of caustic alkali in asecond or subsidiary vessel, separated from the main vessel by a porous partition, thus setting free in themain vessel chlorin corresponding to the alkali produced in the second orsubsidiary vessehsuch chlorin being mostly dissolved by the electrolytic liquor in the main vessel and reactvessel l), while in Fig. 2 it is outside vessel Z1,

part of the wall of which at c is of porousmaterial, as is the wall of the subsidiary vessel c in Fig. l.

The current entering by anode d is divided into two parts, the larger portion leaving by cathode e and the smaller portion passing through the porous Wall c to subsidiary cathode f. As an example, one thousand amperes may be passing from d and only nine hundred and fifty amperes leaving by cathode e and lift-y amperes by f. Thus the electrolyte in b is subjected to greater action at anode ol than at cathode e. With this construction it Will be obvious that the quantity of chlorin liberated at anode d is chemically equivalent to the sum of the alkali formed at cathode e, together with that formed in subsidiary vessel ct at cathode f.

The vessel l) is made of acid-resisting material and the anode and cathodes of material which vwill resist the action of the electrolytes.

As an example, it may be stated that goed results can be attained when the porous wall or diaphragm c is composed of the usual porous earthenware, although it will be obvious that it is preferable to employ a kind which will best resist the action of both acid and alkali, and the strength of the latter in vessel ct may be kept within any desired limits by its more or less continuous withdrawal, coupled with the admissionof' a corresponding quantity of fresh chlorid solution.

The anode d is preferably made of platinum or platinum alloys, 'and the cathode e maybe made of the same materials or may be of carbon, while the cathode f, being practically only subjected to the action of hydrogen and alkali, may be made of any suitable substance-say iron or carbon.

When starting the process, the electrolyte in vessels a and b is composed of a solution of one or more of the alkali chlorids, from which it is preferable to rst remove the salts of lime, magnesium, and iron, and this may be done by boiling the crude chlorids With alkaline carbonate, to which a little free alkali may be added, if desired, and for this purpose the liquors from the subsidiary vessel a after electrolysis are verysuitable, especially when partiallyor wholly converted into carbonate in the usual manner.

The fundamental reaction when electrolyzing chlorid-of-sodium solution, for example, is that chlorin is set free at the anode and metallic sodium is formed at the cathode. The sodium, however, in the presence of water combines with same and forms sodium hydroxid, which in the presence of free chlorin generated at the anode and dissolved in the solution is converted into hypochlorite and chlorid of sodium, all these reactions being well known and the solution remaining practically neutral.

When the current passes, free chlorin is liberated at anode CZ to an extent equivalent to the alkali separated in vessel a, and this acts on the hypochlorite of the alkali metal, which is always present during the formation of chlorate in the main volume of liquor, which is kept agitated and in circulation by the great evolution of hydrogen taking place at the main cathode. The reaction which occurs may probably be represented by the following equation, R being used to designate one atom of an alkali metal s' RClO+H2O-{2Cl:ROl-{2HO1O and whether this correctly represents the process or not the effect is to keep the main liquor in good Working condition.

The presence of free hypochlorous acid in the solution assists in the rapid formation of chlorates, as it is known that such acid being more unstable than its salts is of itself rapidly converted into chloric acid, which in turn reacts with the alkaline hypochlorite, forming chlorate and setting free more hypochlorous acid when the cycle of reactions is again repeated. The reactions taking place in vessel b are probably as follows: by electrolysis R denoting one atom of an alkali metal, as above stated.

RCL-R+ 01(1) 2R+2H2o=2RoH+H2(2) 2ROI-I-l-2Cl=ROCl+RCl-|-H2O(3). Then, as above stated, there being in accordance with this invention an excess of chlorin Ro1o+rr2o+2o1=Rc1+2Ho1o(4), HOlO spontaneously breaks up, so far as is known, as follows:

reactions 5 and 6 being continuously repeated so long as the process is continued.

The magnitude and duration of the current passing between the electrodes d and f is adjusted by testing the hypochlorite oxygen in the main cell b in the usual manner by means of sodium arsenite. This hypochlorite oxygen must be kept below about one gram per liter, and this can be brought about without any serious evolution of chlorin when the agitation is sufficient. If it is found more convenient, the acidity of the liquors can be estimated after conversion of the hypochlorous acid by neutral hydrogen peroxid into hydro; chloric acid, using phenolpthalein as an indicator. A correct degree of acidity is about two grams H010 per liter.

The cathode f is connected through a regulating variable resistance g and switch h with the connection from cathode e, thus enabling the action in the subsidiary vessel a to be stopped or varied from time to time as may be desired. The electrolyte in the main vessel. b is from time to time saturated with fresh chlorid after the chlorate or perchlorate has been extracted, and the liquor in vessel a is replaced by fresh liquor as often as may be convenient.

As an example, it may be stated that good results have been obtained with an electrolytic bath of about three hundred liters of saturated chlorid-of-sodium solutionin vessel b and a circulating electrolyte of about ten liters per hour of a similar solution in vessel a. The current at anode d, being one thousand amperes, is divided, about nine hundred and fty passing to cathode e'and fty through the porous partition c to cathode f. After such current has been passing for about one hour it will be found that the elec'- trolyte in b contains about the requisite quantity of hypochlorous acid to enable approximating to ninety per cent. of the theoretical yield of chlorate obtainable from the current employed to be secured or, say, about five hundred and ninety-seven grams of chlorate produced per thousand ampere hours.

What I claim isl. Theimproved method of manufacturing chlorates and perchlorates of the alkali met als consisting of subjecting the electrolyte from which such substances are to be derived, to unequal electrolytic action at the anode and main cathode respectively, the action at the anode being the greater, substantially for the purposes set forth.

2. The improved method of manufacturing chlorates and perchlorates of the alkali metals consisting of subjecting the electrolyte from which such substances are to be derived to unequal electrolytic action at the anode and main cathode, the action at the anode being the greater and diverting the excess quantity of current to a subsidiary vessel containing a cathode and an electrolyte, substantially as and for the purposes set forth.

3. The improved method of manufacturing chlorates and perchlorates of the alkali met` als consisting of subjecting the electrolyte from which such substances are to be de- IOG rig

lived to the action of an electric current, dverting a portion of the current to a subsidiary vessel containing a cathode and an electrolyte and producing therein an alkaline solution and at the same time producing a corresponding amount of ehlorin in the main electrolyte substantially as and for the purposes set forth.

In testimony whereof I halve hereunto set my hand in the presence of two subscribing Io Witnesses.

RICHARD THRELFALL.

Witnesses:

PHILIP M. JUSTICE, WALTER J. SKERTEN. 

